This invention relates to an improved guard mechanism for the cable of a ski lift system to prevent dislocation or dislodgement of the wire rope from the pulley wheels or sheaves at tower stations. The problem of deropement has become particularly acute in recent years as certain disasters resulting in loss of life have renewed a focus on the safety of lift systems. In particular, this invention is directed to an improved star guard mechanism to prevent deropement at tower stations as the connecting support of the chair or gondola passes over the tower breakover sheaves. The improved star guard has a four finger, self indexing mechanism, with provision for reducing the impact of the horizontal cross bar connecting the wire rope to the chair or gondola support of a lift system.
Because of the frequent problems of icing of the lift system, a guard mechanism should be designed with as few moving parts as possible in order to provide for free rotation of the star guard both during start-up and during operation. Further, due to the obvious inclement weather conditions encountered at the high elevations of ski resorts, a safety system should be constructed to function faultlessly during the most adverse of weather conditions.
Prior systems have been proposed which utilize an auxilliary star guard to the rope carrying sheaves or breakover sheaves. However, such systems have certain defects which can cause a malfunction, that may in fact result in the rope being displaced from the line sheaves which is the very event sought to be prevented.
For example, in star guard systems having more than four fingers or lobes, the clearance provided by the next following finger or fingers with respect to the connecting cross arm of the next advancing chair or gondola, is reduced to an unacceptable level. Further, the angle of attack of the subsequent finger is such that a slight dislocation will render it capable of hitting the advancing cross arm on end with undesirable results. Such systems with more than four fingers have been proposed in Moser, U.S. Pat. No. 4,226,187, issued Oct. 7, 1980, and in Marain et al., French Pat. No. 2,389,523 (1976).
It has been discovered that a four lobe star of proper design can provide all of the guard protection of stars with greater numbers of fingers without the disadvantages of such prior systems. While a four lobe system has been proposed in the past in Lenoble, French Pat. No. 817,506 (1937), the particular configurations of the lobes are such that they are excessively wide, each covering greater than an octant, with blunt ends resulting in diminished clearance between lobes. The wide lobes form an effective attack angle and blunt end that can result in jamming. Additionally, even during normal index positioning the angle of attack on impact of the lobes, tends to lift the actuating cross bar and connected cable, which is undesirable if the guard becomes frozen or locked in position.
Because it is desirable to have the star guard maintained in an indexed preset condition, various devices have been proposed to accomplish this positioning. In the French system of Marian et al. a detent mechanism with a spring loaded ball, acting on grooves in the star guard hub provides for a stepping action on indexing. This mechanism, however, results in excessive drag increasing the impact of the cross bar on the fingers during initial indexing. Further, the mechanism is subject to either jamming or operational failure by icing. Similarly, the French system of Lenoble utilizes a leaf spring and square cam to maintain indexed orientation. This mechanism, being exposed, is also subject to icing and malfunction.
The guard system devised solves the problems of prior systems and provides a four lobe or finger star guard that minimizes the possibilities for failure and minimizes the force of impact of the crossbar with the guard lobes, reducing noise and wear.